The present invention relates to a safety device for a motor vehicle.
Nothing in the following discussion of the state of the art is to be construed as an admission of prior art.
Bumper systems, i.e. bumper beams, are generally sized to conform to the standards of the Allianz Zentrum für Technik [Allianz Center for Technique] with respect to high-speed crashes. As a consequence, metal parts are used that are relatively stiff at speeds of above 20 km/h; However, these metal parts pose an increased risk of injury for pedestrians. A shock absorbing action in the event of an impact with a pedestrian is realized only across the outer skin and the subjacent foams which absorb part of the impact energy in the area of the bumper. When newly developed vehicles are involved, the legal load limit values for the various body areas of a pedestrian are tested within the framework of defined Euro-NCAP tests. Therefore, the automobile industry strives to identify and optimize the relevant impact zones.
To reduce the risk of injury of a pedestrian in the event of a collision with a passenger car in a speed range of 20 km/h to 50 km/h, the supporting vehicle front structure should be constructed as soft as possible. However, a soft design of the vehicle front runs counter to the demands to provide a protection of vehicle occupants in the event of a crash at high speed because such a crash requires a maximum energy absorption in the area of the front structure. The required foam elements in the area of the bumpers have limited energy absorption capability which is exhausted when high speeds are involved.
Another consideration is the direct effect of the required thickness of the foam material on the design and length of the front structure of the vehicle. Construction-based changes in design are undesired as are vehicles of excess length.
It has also been proposed to utilize the space inside the side rail by allowing the deformation elements which are arranged between side rail and bumper beam, to move into the side rail. Examples include international publication no. WO 99/15364 or U.S. Pat. No. 3,633,934, which disclose telescoping shock absorbers which move into the side rails in the event of an impact. German Offenlegungsschrift DE 42 38 631 A1 describe a shock absorbing structure having inner and outer tubes which can move within one another, with the outer tube being supported on the side rail by a flange. Even though these types of deformation elements address the shock absorbing behavior, it is still complicated to provide a deformation element which is able to absorb a high-speed crash, e.g. 60 kN to 110 kN, depending on vehicle and manufacturer, and yet has a rigidness of only few newtons for a frontal impact of a pedestrian, i.e. a rigidness that is smaller by several powers to ten. An example for an energy absorbing device which can be blocked in dependence on the impact speed is disclosed in German Offenlegungsschrift DE 10 2004 059 545 A1.
It would be desirable and advantageous to provide an improved safety device for a motor vehicle to obviate prior art shortcomings.